1. Field of the Invention
The present invention relates to an exposure apparatus, specifically, to an exposure apparatus for exposing a photosensitive material to light emitted from an array of light emitting elements.
2. Description of the Related Art
An organic EL (electroluminescent) element using a fluorescent organic material as a light emitting layer has the advantages that it can be manufactured more easily than other light emitting elements, it can constitute a thin and lightweight light emitting device, etc., and thereby, research and development as a thin display element has been conventionally promoted. Recently, since an organic EL element achieving high performance also in luminous brightness, luminous efficiency, and durability comparable to a light emitting diode (LED) has been obtained, application to an exposure apparatus for exposing a photosensitive material such as a silver halide photosensitive material is under study.
As shown in FIG. 12, for example, an exposure apparatus using organic EL elements comprises an organic EL element array in which plural sets (two sets in FIG. 12) of rows of elements, which are formed by arranging plural organic EL elements 80 emitting light in respective colors of red (R), green (G), and blue (B) with respect to each color along a main scanning direction, are arranged in a sub scanning direction with the rows of elements of three colors R, G, and B as a set. Note that, in FIG. 12, the organic EL elements 80 of the respective colors R, G, and B are shown by being assigned with letters of the alphabet (R/G/B) indicating corresponding colors at ends of signs for distinction. A latent image of a full color image is formed by moving this exposure apparatus relative to a photosensitive material.
The luminous intensities of the organic EL elements 80R, 80G, and 80B of the respective colors R, G, and B are determined according to exposure sensitivity of the photosensitive material. However, in the case where luminous intensities are different among elements that constitute the organic EL element array, a difference is caused in degradation amounts, and color tone is drifted out gradually (color balance is deteriorated) with use of the exposure apparatus. As a result, a method for making the magnitude of degradation constant by using an organic element array, in which a number of white organic EL elements that have substantially the same light amount of emission are arranged, and color filters of the respective colors R, G, and B for optimizing the exposure amounts with respect to each color by adjusting transmittance has been proposed (for example, see Japanese Patent Laid-Open (JP-A) No. 2000-103114, Paragraph 0026). This method is based on the concept that white organic EL elements constituted by the same material have the same degradation rate and degradation amount.
Here, the relationship between emission spectral intensity of an organic EL element and spectral sensitivity of a photosensitive material is discussed. FIG. 13A shows emission spectral intensity of a white organic EL element, FIG. 13B shows spectral transmittance of a color filter, and FIG. 13C shows exposure spectral intensity for exposing the photosensitive material to light. Further, FIG. 13D shows spectral sensitivity of a silver halide photosensitive material (negative type) for general photographs, and FIG. 13E shows color optical density of the photosensitive material.
The color optical densities (Dr, Dg, Db) of the photosensitive material in the respective colors shown in FIG. 13E are derived by multiplying “exposure spectral intensity” shown in FIG. 13C and “spectral sensitivity of photosensitive material” shown in FIG. 13D and integrating with respect to wavelength, as expressed by the following equation.densities of respective colors (Dr, Dg, Db)=∫(exposure spectral intensity×spectral sensitivity of photosensitive material)dλ
In addition, the exposure spectral intensity shown in FIG. 13C is a product of “emission spectral intensity” shown in FIG. 13A and “spectral transmittance of filter” shown in FIG. 13B. Therefore, the respective color optical densities of the photosensitive material are expressed by the following equation.densities of respective colors (Dr, Dg, Db)=∫(emission spectral intensity×spectral transmittance of filter×spectral sensitivity of photosensitive material)dλ
However, as seen from FIGS. 13A to 13E, the silver halide photosensitive material for general photographs has sensitivity to R, G, and B light as R:G:B≈1:10:70, and the sensitivity ratio greatly differs. Therefore, in the case where the exposure amount is optimized with respect to each of the colors R, G, and B by adjusting transmittance by color filters, there is no choice but to match the amount of light to that of R color of the lowest sensitivity. Therefore, in the case where the method disclosed in Japanese Patent Laid-Open (JP-A) No. 2000-103114, Paragraph 0026 is applied to the photosensitive material having an extreme variance in sensitivity ratio between R, G, and B such as the photosensitive material for general photographs, energy utilization efficiency becomes extremely low.
Further, even if the same types of organic EL elements are used, in the case where the multiple exposure sequence, in which multiple tone exposure is carried out by exposing the same pixel to light a number of times, is performed, a difference is caused in at least one of the luminous intensity and the emission time among the elements that constitute the organic EL element array. If the luminous intensity is the same, but the emission time is different, the cumulative emission amounts of the respective elements become different, and thereby, a difference in the degradation amount is caused. As a result, there is a problem that the luminous intensity varies among the elements that constitute the organic EL element array to generate streaks and deteriorate color balance, as shown in FIG. 14. Especially, in the case where the same image is exposed to light a number of times, the emission amounts of the organic EL elements in certain positions become larger and a significant difference in degradation amount is caused among elements.
On the other hand, in order to deal with the above described problems, it is conceivable that the above described luminous intensities may be made constant by correcting light amounts of the individual organic EL elements. However, there is a problem that a complex apparatus is required in order to measure and correct the light amounts of several thousands to several millions of organic EL elements one by one, and the cost of the apparatus increases proportionately. Further, there is another problem that the time required for correction becomes longer and the productivity becomes lower.
Thus, there is a need in the art to solve the above described problems, and an object of the invention is to provide an exposure apparatus capable of suppressing the deviation of the color balance by a simple construction. In addition, another object of the invention is to provide an exposure apparatus capable of implementing exposure with high energy utilization efficiency.